The invention relates generally to the field of magnetic bubble technology (MBT) and, more particularly, to means for propagating or transmitting magnetic bubbles, especially in recirculating closed loops.
MBT involves the creation and manipulation of magnetic bubbles in specially prepared magnetic materials. The word "bubble", used throughout this text is intended to encompass any single-walled magnetic domain, defined as a domain having an outer boundary which closes on itself. The application of a static, uniform magnetic bias field orthogonal to a sheet of magnetic material having suitable uniaxial anisotropy causes the normally random serpentine pattern of magnetic domains to shrink into isolated, short cylindrical configurations or bubbles whose common polarity is opposite that of the bias field. The bubbles repell each other and can be moved or propagated by a magnetic field in the plane of the sheet.
Many schemes exist for propagating bubbles along predetermined channels. These techniques can be classed generally as conductor-accessed and field-accessed. In conductor-accessed propagation systems electrically pulsed conductive loops are disposed in series over the magnetic sheet. In field-accessed propagation systems electrical conductors are not disposed on the magnetic sheet for propagation; instead, an overlay pattern of ferromagnetic elements establishes a bubble propagation channel in which a sequence of attracting poles is caused to be formed in the presence of a continuous, uniformly rotating magnetic drive field in the plane of the sheet.
A major distinction in function between conductor-accessed and field-accessed circuits is that several conductor-accessed circuits can be disposed on the same sheet or "bubble chip" and operated completely separately and exclusively from each other while field-accessed circuits on the same chip all operate at the same time under the control of a ubiquitous, uniformly rotating, common drive field.
One attempt at providing field-accessed channel selection is shown in U.S. Pat. No. 3,543,252 to Perneski illustrating several variations on the familiar T-bar circuit to which different permutations of pulsed orthogonal drive fields are applied.
MBT can be used in data processing because magnetic bubbles can be propagated through channels, whether field-accessed or conductor-accessed, at a precisely determined rate so that uniform data streams of bubbles are possible in which the presence or absence of a bubble at a particular position within the stream indicates a binary "1" or "0". Because of its potential for low cost, low power consumption and extremely high bit density, MBT is under active consideration for use in large scale memories of moderate speed. One of the prime design elements of many memory systems utilizing field-accessed magnetic bubbles is the provision of a closed loop bubble path which can be used as a recirculating "shift register". Many memory arrangements of this type employ a plurality of "minor" loops selectively interconnectible with a "major" loop such that bubbles can be transferred between the major and minor loops on command. The ability to propagate bubbles in one or more recirculating loops without operating other loops on the same chip has until recently been confined to systems employing conductor-accessed circuits. Mutually exclusive closed loop field-accessed bubble propagation circuits are disclosed in copending application Ser. No. 432,450, filed Jan. 11, 1974, by Howard H. Aiken, Paul T. Bailey and Robert C. Minnick, entitled "Mutually Exclusive Magnetic Bubble Propagation Circuits". Discrete mutually exclusive circuit elements and systems composed thereof are disclosed in copending application Ser. No. 448,649, filed Mar. 6, 1974, by Paul T. Bailey and L. John Doerr III, entitled "Mutually Exclusive Magnetic Bubble Propagation Circuits With Discrete Elements" now U.S. Pat. No. 3,879,716. Both of the aforementioned copending applications are assigned to the assignee of this application and incorporated herein by reference.
One of the features of the closed loop embodiments disclosed in the aforementioned copending applications is that the sides of each circuit must be parallel to corresponding sides of a reference triangle, preferably equilateral. Consequently, the embodiments therein disclosed did not have the geometry of a rectangle or parallelogram. This feature may be a disadvantage in applications where complex circuit paths become necessary to conserve space on the bubble chip.